The descriptions in this section merely provide background information related to the present disclosure, which may not necessarily constitute the prior art.
As shown in FIG. 1, a conventional scroll compressor 100 generally includes a housing 110, a top cover 112 provided at one end of the housing 110, a bottom cover 114 provided at the other end of the housing 110, and a partition plate 116 which is provided between the top cover 112 and the housing 110 so as to divide an interior space of the compressor into a high-pressure side and a low-pressure side. The high-pressure side is defined between the partition plate 116 and the top cover 112, and the low-pressure side is defined among the partition plate 116, the housing 110 and the bottom cover 114. An inlet 118 for inflowing the fluid is provided on the low-pressure side, and an outlet 119 for discharging the compressed fluid is provided on the high-pressure side. An electric motor 120, including a stator 122 and a rotor 124, is provided in the housing 110. A driving shaft 130 is provided in the rotor 124 to drive a compression mechanism including a fixed scroll 150 and a movable scroll 160. The movable scroll 160 includes an end plate 164, a hub portion 162 formed on one side of the end plate and a spiral wrap 166 formed on the other side of the end plate. The fixed scroll 150 includes an end plate 154, a spiral wrap 156 formed on one side of the end plate and a discharge port 152 formed approximately at the center of the end plate. A series of compression pockets C1, C2 and C3, the volumes of which are reduced from outside to inside in a radial direction, are formed between the spiral wrap 156 of the fixed scroll 150 and the spiral wrap 166 of the movable scroll 160. The radial outermost compression pocket C1 side is at the intake pressure, and the radial innermost compression pocket C3 side is at the discharge pressure. The intermediate compression pocket C2 is between the intake pressure and the discharge pressure, thereby being also called a medium pressure pocket.
The movable scroll 160 is supported at one side by the upper portion of a main bearing housing 140 (which forms a thrust member), and the driving shaft 130 is supported at one end by a main bearing 144 provided in the main bearing housing 140. An eccentric crank pin 132 is provided on one end of the driving shaft 130, and an unloading bushing 142 is provided between the eccentric crank pin 132 and the hub portion 162 of the movable scroll 160. Under the driving of the motor 120, the movable scroll 160 will orbit relative to the fixed scroll 150 (i.e., a central axis of the movable scroll 160 rotates about a central axis of the fixed scroll 150, but the movable scroll 160 does not rotate about its own central axis) to compress fluid. The orbiting is achieved through an Oldham coupling 190 disposed between the fixed scroll 150 and the movable scroll 160. The fluid compressed by the fixed scroll 150 and the movable scroll 160 is discharged to the high-pressure side through the discharge port 152. To prevent the backflow of the fluid at the high-pressure side to the low-pressure side via the discharge port 152 in particular cases, a check valve or discharge valve 170 is provided at the discharge port 152.
To compress fluid, it is necessary to have an effective seal between the fixed scroll 150 and the movable scroll 160. On the one hand, it is necessary to have an axial seal between a top end of the spiral wrap 156 of the fixed scroll 150 and the end plate 164 of the movable scroll 160 and between a top end of the spiral wrap 166 of the movable scroll 160 and the end plate 154 of the fixed scroll 150.
Generally, a backpressure pocket 158 is provided on the side of the end plate 154 of the fixed scroll 150 opposite to the spiral wrap 156. A seal assembly 180 is provided in the backpressure pocket 158, and the partition plate 116 limits an axial displacement of the seal assembly 180. The backpressure pocket 158 is in fluid communication with the intermediate pressure pocket C2 through an axially extending through-hole (not shown) formed in the end plate 154 so as to generate a force for pressing the fixed scroll 150 towards the movable scroll 160. Since the movable scroll 160 is supported at one side by the upper portion of the main bearing housing 140, the pressure in the backpressure pocket 158 may be applied to effectively press the fixed scroll 150 and the movable scroll 160 towards each other. When the pressures in various compression pockets exceed a predetermined value, the resultant force generated from the pressures in the compression pockets will larger than the downward pressing force provided in the backpressure pocket 158 so as to allow the fixed scroll 150 to move upwardly. At this time, the fluid in the compression pockets will leak to the low-pressure side for unloading through a gap between the top end of the spiral wrap 156 of the fixed scroll 150 and the end plate 164 of the movable scroll 160 and a gap between the top end of the spiral wrap 166 of the movable scroll 160 and the end plate 154 of the fixed scroll 150, thereby providing an axial flexibility for the scroll compressor.
On the other hand, it is necessary to have a radial seal between a side surface of the spiral wrap 156 of the fixed scroll 150 and a side surface of the spiral wrap 166 of the movable scroll 160. Such radial seal between them is generally achieved by means of a centrifugal force of the movable scroll 160 in operation and a driving force provided by the driving shaft 130. Specifically, in operation, under the driving of the electric motor 120, the movable scroll 160 will orbit relative to the fixed scroll 150 (i.e., a central axis of the movable scroll 160 rotates about a central axis of the fixed scroll 150, but the movable scroll 160 does not rotate about its own central axis), and thus will generate the centrifugal force. Additionally, the eccentric crank pin 132 of the driving shaft 130 may generate a driving force component contributing to achieve the radial seal between the fixed scroll and the movable scroll during rotation. The spiral wrap 166 of the movable scroll 160 will be brought into abutment against the spiral wrap 156 of the fixed scroll 150 by means of the centrifugal force and the driving force component, thereby achieving a radial seal between them. When incompressible materials (such as solid impurities, lubricating oil and liquid refrigerant) enter the compression pocket and get stuck between the spiral wrap 156 and the spiral wrap 166, the spiral wrap 156 and the spiral wrap 166 may temporarily separate from each other in the radial direction to allow foreign matters to pass therethrough, thereby preventing the damage of the spiral wrap 156 or 166. This ability to radially separate provides a radial flexible for the scroll compressor, improving the reliability of the compressor.
However, there are the following problems as a result of the radial seal achieved by the centrifugal force as described above. FIG. 2 shows a schematic view of a radial seal force between a fixed scroll 150 and a movable scroll 160. As shown in FIG. 2, a total radial seal force between the fixed scroll 150 and the movable scroll 160 may be represented by the formula:Fflank=FIOS+Fs Sin θeff−FIO*Sin θ−Frg  formula (1)
where
Fflank is a total radial seal force between the fixed scroll 150 and the movable scroll 160;
FIOS is the centrifugal force of the movable scroll 160;
Fs Sin θeff is the driving force component provided by the eccentric crank pin 132, wherein Fs is the total driving force provided by the eccentric crank pin 132, and θeff is the effective driving angle of the eccentric crank pin 132;
FIO*Sin θ is the centrifugal force component provided by the Oldham coupling 190, wherein FIO is the total centrifugal force provided by the Oldham coupling 190, θ is an angle of the movable scroll 160 oriented relative to the fixed scroll 150;
Frg is the radial gas force provided by the fluid in the compression pockets.
As can be seen from the above formula 1, FIOS and FIO*Sin θ are items related to the rotational speed of the driving shaft 130, whereas Fs Sin θeff and Frg are items independent of the rotational speed of the driving shaft 130. Thus, the radial seal force Fflank is related to the rotational speed of the driving shaft 130. That is, the greater the rotational speed of the driving shaft 130 is, the greater the radial seal force Fflank is, and the smaller the rotational speed of the driving shaft 130 is, the smaller the radial seal force Fflank is. Therefore, when the scroll compressor 100 is operated at a low rotational speed, the radial seal force Fflank between the fixed scroll 150 and the movable scroll 160 may be insufficient, thereby resulting in a reduced efficiency of the compressor, whereas when the scroll compressor 100 is operated at a high rotational speed, the radial seal force Fflank between the fixed scroll 150 and the movable scroll 160 may be excessively large, thereby causing an excessive wear of the scroll components.
Therefore, there is a need for a scroll compressor which can ensure a radial seal both at a low speed and at a high speed in operation.